A comparison of the proteolytic enzymes involves in hemoglobin digestion has been made using a chloroquine (pigmented) sensitive and chloroquine resistant (non-pigmented )strain of Plasmodium berghei. The chloroquine sensitive (pigmented) strain contains a parasite specific enzyme that is found neither in the host cell (erythrocyte or reticulocyte) nor in the chloroquine resistant strain. The chloroquine resistant strain appears not to possess its own enzyme as extracts contain only activities identical to those of the non-infected reticulocyte. Work comparing the chloroquine sensitive and chloroquine resistant Plasmodium falciparum is currently in progress. Studies on the effects of various protease inhibitors on invasion of the erythrocyte by the malaria parasite indicate that the chymostatin at 50 to 100 micromolar concentrations significantly reduces invasion. It appears non-toxic in so far as attachment may occur. Other inhibitors including antipain, PMSF, and pepstatin have no effect. The data suggests that proteolytic enzymes may play a role in invasion. Studies are underway to identify and characterize these enzymes.